Medical devices such as wires, guide wires, probes, mandrels, needles, cannulas, and other medical devices are commonly inserted into humans or animals for therapeutic and diagnostic medical procedures. Often, surgeons or other medical professionals must be able to determine the specific distance that a medical device is inserted into a body. The accurate placement of the medical device is often critical to the procedure. If a medical device is inserted too far into a patient, it could tear, puncture, or otherwise cause damage to internal bodily tissues, vessels, and other organs, which could be harmful or potentially fatal to the patient. Alternatively, if not inserted far enough, the procedure may not be successfully performed. Accordingly, certain medical devices are marked with visual indicia at measured intervals along the length of the device to indicate the length of the medical device inserted into a patient.
Additionally, many medical devices are coated with one or more low friction materials such as polytetrafluoroethylene (PTFE). Low friction coatings reduce the amount of friction between the medical device and bodily tissues, catheters, or other surfaces. Without low friction coatings, certain medical devices are more likely to “stick” to tissues, catheters, or other surfaces during insertion or extraction. If a medical device sticks to other surfaces as it is inserted into a body, a surgeon or other medical professional must apply a greater insertion force to the medical device to reinitiate movement. Once movement is reinitiated, the opposing force immediately decreases so that the medical device is caused to quickly accelerate into the body. Such extreme movements increase the risk of scraping, rubbing, tearing, puncturing, or otherwise damaging a patient's internal tissues due to misplacing the end of the device in the patient. Low friction coatings are less likely to stick to other surfaces and therefore give surgeons or other medical professionals more control or modulate over the insertion speed and depth, which reduces the risk of damage to the patient, thus reducing the “slip-stick” phenomena. Additionally, low friction coatings generally have smooth surfaces that will not scrape, irritate, or snag tissues, vessels or arteries. However, there are very limited methods for marking such devices with low friction coatings.
One known method of marking low friction coated medical devices is to grind, ablate or acid remove the low friction coating to expose the surface of the medical device so that the contrast between the color of the low friction coating and the base metal or surface of the medical device can serve as visual indicia. Ablation is typically achieved by using corrosive chemicals or laser beams, or grinding or grit blasting to selectively remove the coating from the medical device. Such ablation or grinding methods remove the entire coating from the surface of the device, which creates grooves or valleys in the surface of the low-friction or other coating. The shoulders of these grooves or valleys can have sharp edges, particularly when laser beams, grinding, or other similar techniques are used to remove the coating. The resulting sharp edges can scrape bodily tissues, snag vessels or arteries of the patient, or otherwise cause damage and/or trauma to the patient. When inserting medical devices into delicate areas such as the brain and heart, damage caused by the sharp shoulders of the grooves or valleys can be harmful and potentially fatal for the patient. Even if the shoulders are shaped to reduce or eliminate sharp edges, this method of marking low friction coated medical devices still removes the benefits of the low friction coating and exposes the raw, unprotected surface of the medical device, particularly when a wire device changes directions or goes around a turn in a vessel, vein or artery. As described above, the exposed surface of the medical device is more likely to stick to bodily tissues and other surfaces, potentially harming the patient. Additionally, this method of marking low friction coated medical devices creates different diameters along the length of the medical device which can also increase the required insertion force and decrease the control a surgeon or other medical professional can exercise over the speed and depth of an insertion. Therefore, the above method of marking low friction coated medical devices adversely affects the function of the coated medical device and can increase the risk of injury to a patient.
Another known method of marking low friction coated medical devices is to print ink on the surface of the coating. However, low friction coatings resist bonding with inks, and inks printed on low friction coatings may peel off and be left inside the patient's body, which may harm the patient. Ink may also rub or peel off before or during use of the medical device, thus destroying the usefulness of the markings, and increasing the risk that the medical device will be inserted either too deep, or not deep enough (and harm the patient and/or render the medical procedure ineffective). Furthermore, many medical devices have small diameters such that even thin layers of ink can significantly increase the diameter of the device, which, as previously described, is undesirable.
Marking low friction coated medical guide wires poses additional problems. Medical guide wires are generally shaped like coiled springs, having an elongated strand of medical wire helically wound such that adjacent turns of the wire are in contact with each other. Known methods of marking low friction coated medical guide wires, such as grinding or ablating the coating to expose the surface of the medical guide wire each have the disadvantages of either increasing or decreasing the diameter of the medical guide wire and/or removing the low friction coating, which is undesirable. Removal of the coating by mechanical processes such as by grinding or using abrasives could possibly weaken the thin wire that forms the coils of the medical guide wire. Laser ablation does not harm the wire, however it removes the low friction coating which is undesirable. Additionally, despite repeated rinsing, material removed from the coating can get caught between the turns or adjacent segments of the medical wire and can be deposited in a patient's body during a medical procedure, which could be potentially fatal for the patient. Furthermore, marking the coated medical guide wire with paint is not effective because paint will easily crack and delaminate between adjacent turns of the medical guide wire and the paint could be deposited in a patient's body, which could also be harmful and potentially fatal for the patient.
One known method of forming a low-friction coating on a medical device includes applying an aqueous PTFE solution to the surface of a medical device. The solution includes particles of a low friction material such as PTFE, an acid such as chromic acid, a pigment, wetting agents, other ingredients, and water. The solution is cured at a high temperature such as 750° F. (399° C.) to cure the coating. The pigments used in this method are generally stable at temperatures exceeding the cure temperature so that they do not shift color during the curing process. Although the pigments used in this method generally will shift color at temperatures above the cure temperature, when heated to such temperatures the low friction character of the PTFE coating permanently degrades and the bonds between the low friction coating and the medical device weaken, which destroys the coating adhesion and utility of the low friction coating.
Accordingly, a need exists for improved markings on medical devices, and specifically medical wires or tube type devices with low friction coatings. Such a need exists for medical devices with markings that do not significantly increase or decrease the diameter of the medical device, or significantly adversely affect the function of the low friction coating.